Strain relief for electrical appliance cord sets



Dec. 31, 1940; H. w. HEYMAN STRAIN RELIEF FOR ELECTRICAL APPLIANCE CORD SETS Filed March 8, 1940 INVENTOR 1 555666 7l/flg'yzrgdzz" BY $7M AT foRNEY Patented Dec. 31, 1940 I UNITED STATES PATENT OFFICB STRAIN RELIEF FOR ELECTRICAL APPLIANCE CORD SETS Horace Heyman, Kenilworth, N. J. Application March a, 1940, Serial No. 322,906

Claims. (Cl. 173-322) This invention relates to means for relieving Figure 3 is a plan view on an enlarged scale of the strain on an electrical cord or cable used with the metallic member forming the strain-relief various electrical appliances such as fiat irons device in its initially constructed state. and toasters. Figure 4 is a side view of Figure 3, looking to- In the construction of a plug for household ward the split side of the device.

' electrical appliances the plug is usually made As shown in the various views, I and 2 illuswith an annular recess at one end, through trate the two halves of a plug which is moulded which the cord passes. This annular recess is from any suitable material, the two halves prefordinarily used for the reception of a protecting erably being identical so that when put together 10 spring which is used around the plug end of the and. held in any satisfactory manner, as by screws 10 cord. After passing through this annular recess, which may be passed through the holes 3 and 4, the conductors of the cord are split and pass on the cord is held in working relation with the opposite sides around what may be termed a two parts of the plug.

. divider, to their respective contact terminals My improved form of strain-relief device compositioned in recesses formed in the two halves prises a metallic member, which has consider- 15 of the plug. able stiffness, having .a, collar portion 5 and an In certain of these appliances, if used for a integral flange portion 6. The flange 6 is prefconsiderable length of time, as in the case of a erably provided with a plurality of lugs 1 and 8 fiat iron, the plug may become quite hot and which are adapted to be positioned in oppositely the operator, in pulling out the plug, would take disposed pockets formed by recesses 9 and In in 20 hold of the 'cord and give it a yank. This puts each of the plug halves I and 2, the depth of the a highly detrimental strain on the conductors of pockets being just sufficient to accommodate the the cord and tends to break the conductors or width of the lugs I and 8. This prevents the pull them loose from their terminals, with the strain-relief device member from turning in the danger of causing a short circuit, thereby introannular recess II formed in the two parts of the 25 ducing a fire hazard. plug. The strain-relief member is initially The Underwriters Laboratories now require formed with the collar and flange portions 5 and that the cord of an appliance set shall be capa- 6 split, with an opening I: such as to accommoble of withstanding for aperiod'of about one date the usual braided rubber-covered cord I3.

minute a straight pull of fifty pounds between Preferably, I use, as a reenforcing member be- 30 the cord and plug, with the cord conductors tween the outer braid of the cord l3 and the inentirely disconnected from their respective terner surface of the collar 5, a strip of insulating minals; also, the cord shall be capable of withmaterial It such as a piece or asbestos tape as standing for a period of one minute a torque of shown in Figure 2. After the strain-relief device three inch-pounds between the cord and the and the tape it have been assembled to thecord 35 ug. in their proper position near the extremities of It is therefore the principal object of my inthe conductor ends, a suitable-molds applied .to vention to provide a strain-relief for the cord the strain-relief device to close the opening I2 which will meet the above requirements with a around the outer periphery of the cord l3, therelarge factor of safety. 1 by very firmly gripping the same, especially when 40 It is a further, object of my invention to proa reenforcing member, such as M, is used. vide a strain relief which may be applied to all To assist in crimping or swedging the strainpresent-day plugs having the said annular recess relief device around the cord to, I prefer to reat the cord end. duce the width of the metal of the flange 6 at the 5 Other and further objects will be apparent to point 85. The flange 6, when crimped or swedged one skilled in this particular art after reading around the'corcl it is of a diameter which will the following specification, taken in connection allow it to be readily placed within the recess with the drawing, wherein: H, and beside acting as a support in the recess Figure 1 is a view on an enlarged scale of the ll for the cord, the flange t also acts as 'a seat two parts of the plug showing the cord in asfor the inner turn I6 of a protecting spring I1, 50

sembled relation with one half of the plug. it being understood that the last one or two in- Figure 2 is a part sectional and part-elevaner turns of the spring I! are of a greater diamtional view through the strain-relief device as eter than the other convolutions of the spring, applied to the cord, at right angle to Figures and nearly equal to the diameter of the recess l or 3. ll, so that the spring I! is securely held in the 55 recess Ii behind the annular shoulder 18 formed by the plug when the two parts are in assembled position.

In Figure 1 I have shown the two conductors l and 20 of the cord as disconnected from their respective terminals 2| and 22, as this illustrates the condition of the cord when ready for the strain and torque tests. If desired, the cord, where the two conductors I9 and 20 separate, may be covered with a binding thread or tape 23 adjacent the end of the divider 24, to prevent the outer braid of the cord from fraying.

In place of a separate reenforcing member l4, which is preferably of insulating material, I may apply to the outer cord of the cable a suitable varnish-like material to strengthen the fibers of the :cord braiding at this point and thereby assure a better grip on the cord by the strain-relief device. Since the strain-relief device per se can be punched and fonmed from sheet metal, such as a suitable grade of steel, and treated with a rust-proof material, it can be made very cheaply, thereby adding little to the expense of the cord set.

What I claim is:

1. In the combination of an appliance cord and plug having interiorly disposed contacts and an annular type recess at the cord end of the plug, strain-relief means for the cord comprising a single-piece metallic member of relatively stiff material having a collar portion to inherently fit tightly around the cord when forced into gripping position around the cord and an integral flange portion to fit in said recess; the collar and flange being of the same angular length by being split at the same place, and the split being initially wide enough to allow the said member to be passed over the cord. I

2. The combination with a cord set comprising a cord and plug, the latter having at the cord end an annular type recess, of strain-relief means located within the recess, said means including at 'least one pocket in the wall of said annular type recess and a single-piece metallic member having inherently good gripping qualities, said member having a collar portion to fit tightly around the cord when assembled thereto, and a flange portion extending integrally with and substantially all the way around the collar to fit in said recess, the collar and flange being co-incidentally split so as to pass the said member over the cord, the flange having a lug positioned in the pocket for preventing the said metallic member from.turning in the recess.

3. The combination with a cord set comprising a cord and plug, the latter having at the cord end an annular type recess, of strain-relief means 10- cated within the recess, said means including arcuately spaced pockets in the wall of said recess and a single-piece metallic member having coincidental, split, collar and flange portions. the latter extending coaxially with the collar and substantially the full angular length thereof, the flange having lugs to flt in said pockets to prevent said metallic member from turning, the collar with its flange being of relatively stiii material so when the said metallic member is placed over the cord by way of the split, and the split ends forced toward each other, the member will, of itself only,

grip the cord.

4. The combination with a cord set comprising a cord and plug, the latter having at the cord end an annular type recess, of strain-relief means located within the recess, said means including at least one pocket in the wall of said annular type recess, a single-piece metallic member having coincidental, split collar and flange portions and a reinforcing means between the metallic member and the cord, the flange of saidmetallic member extending around the collar and having a lug to fit in said pocket to prevent turning of the metallic member in the pocket and also having a part midway between the two split ends somewhat reduced in width to assist in swaging the metallic member around the cord and reinforcing means, the said metallic member being inherently capable alone of tightly gripping the cord and the reinforcing means when the said metallic member is placed over the cord and reinforcing means by way of the split, and the split ends forced toward each other.

5. The combination with an appliance cord and plug, having interiorly disposed contacts and an annular type recess at the cord end of the plug, and a protecting spring member having one end normally positioned in the recess, of strainrelief means for the cord set comprising a singlepiece metallic member of a material having inherent gripping properties and having an integral, co-incidental split collar and flange portions' of substantially the same angular length, together with a separate reinforcement strip to fit between said metallic member and the outer covering of the cord, the split initially being wide enough to allow assembly of the said metallic member over the reinforcement strip and the cord, the flange having means cooperative with means located on the plug for preventing turning of the member in the plug, the flange also acting as a seat for the end of the protecting spring, the collar with its flange being adapted to be closed in to securely grip, by itself alone, the cord substantially as described.

HORACE W. HEYMAN. 

